There is known keratorefractive surgery for ablating a corneal surface with a laser beam in an ultraviolet wavelength range and changing its shape to correct a refractive error of a patient's eye. In a case where even aberration of the eye is to be corrected by the surgery, mainly two methods are used for calculation of a corneal ablation amount.
The first one is a method of obtaining the corneal ablation amount based on measurement data on wavefront aberration in a wide area of the patient's eye. In this method, the corneal ablation amount may be obtained using Expression 1 being an approximate expression which is conventionally known as a processing technique for an optical component.
                              [Expression  1]                ⁢                                  ⁢                  P          ≈                                    δ              ⁢                                                          ⁢              W                                      n              -              1                                                                      
In Expression 1, δW is wavefront aberration, n is a refractive index of an optical component to be corrected, P is a correction amount for a surface.
The second one is, as described in U.S. Pat. No. 6,033,075 (Japanese Patent Application Unexamined Publication No. Hei11-342152) and U.S. Pat. No. 6,086,204, a method of obtaining the corneal ablation amount using measurement data on objective refractive power distribution or that on wavefront aberration distribution in the wide area of the patient's eye, and data on a pre-operative corneal shape.
The corneal ablation amount is obtained by these conventional calculation methods as an ablation amount where the patient's eye is emmetropia with no aberration in a measurement optical axis direction established at the time of the measurement of the objective refractive power distribution or the wavefront aberration distribution (or a non-aberration eye which has particular refractive power in the measurement optical axis direction). However, a human eye is an eccentric optical system comprised of refractive elements such as the cornea and a crystalline lens, and the corneal shape is generally asymmetrical with respect to a visual axis. Therefore, in the conventional calculation methods for the corneal ablation amount, there is a problem that the ablation amount becomes eccentric.
In addition, in the case of additional ablation performed for correcting the patient's eye after the ablation through axial-deviated irradiation of the laser beam, there is a case where a proper corneal ablation amount cannot be obtained with the conventional calculation method for the corneal ablation amount.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a corneal-ablation-data determining apparatus and a corneal-ablation-data determining program capable of controlling corneal ablation amount distribution and expanding ablation applicability.